Cryogenically compatible rocket propellant

ABSTRACT

Propellants for rockets, space transportation vehicles, launch vehicles and systems, crew escape vehicles and systems, launch escape towers, and space vehicle systems are disclosed. Some embodiments provide a rocket propellant comprising a mixture of a small chain alkane from 1 to 4 carbons and a small chain alkene from 3 to 4 carbons. The mixture of the small chain alkane and small chain alkene is in a proportion that lowers the melting of the mixture below the melting point of both the small chain alkane and small chain alkene.

CROSS-RELATED APPLICATIONS

This application claims the benefits of and priority to U.S. patentapplication Ser. No. 15/275,336, filed Sep. 2016, entitled“Cryogenically Compatible Rocket Propellant”, which claims the benefitsof and priority to U.S. Provisional Patent Application Ser. No.62/222,390, filed Sep. 23, 2015, entitled “Reduced-TemperaturePropellant for Rockets and the Like,” which is incorporated byreference.

GOVERNMENT RIGHTS

Some embodiments of this invention were made with government supportunder contract W911NF-16-0097 awarded by the Department of Defense. Thegovernment has certain rights in some embodiments of this invention.

BACKGROUND

Propellants for rockets, space transportation vehicles, launch vehiclesand systems, crew escape vehicles and systems, launch escape towers, andspace vehicle systems and devices are known in the art.

With the rise of the chemical industries of the 19^(th) century,combustion of liquid fuels and oxidizers enabled practicalimplementation of rocket propulsion systems. Starting with acid/analinesand liquid oxygen (LOX)/alcohol and hydrazine/peroxide combinations, theindustry rapidly settled on LOX/liquid hydrogen (LH) and LOX/kerosene.While numerous potential combinations, such as LOX/hydrazine,LOX/methane, were studied, kerosene (RP-1) provided the most energeticcombination and the greatest experience base. However, thermalincompatibility of kerosene to liquid oxygen continue to require complexengineering solutions.

The chemical properties of LOX with almost every practical hydrocarbon(HC), such as methane, butane, benzene, gasoline, alcohol, and ether,have been researched as candidates as a rocket propellant, with mixedresults. While these fuels are economical, the low densities of smallHCs, such as, methane and butane, yield a propellant that is not veryefficient. Recent studies have produced a prototype rocket, which usespropylene as a fuel, however, the studies ended without a viable engine.

In the 1960s, mixtures of methane, ethane, and propane were studied,however, the fuels mixtures required a fluorine-based oxidizer. Thedensity of these mixtures were low, which lowered efficiency, andcreated problems for storage. These fuel mixtures were abandoned, infavor of RP-1.

Although RP-1 with LOX is the preferred rocket propellant, there arestill drawbacks to this combination. For example, after the burn ofRP-1, residue coats the inside of the engine, which needs to be removedto reuse the engine. The residue consists of coke, paraffin, and oils,which are difficult and expensive to remove. If this residue is notcompletely removed, the engine most likely will fail upon reuse.

According to the literature, there has not been a completely new liquidpropellant used in flight in over 30 years. A new rocket propellant,which is economical, burns clean, and has a high density that is similarto RP-1, and has specific impulse equal to or greater than RP-1, isneeded.

SUMMARY

Various embodiments of the present invention, a mixture of propane andpropylene makes an improved rocket fuel by lowering the melting point(freezing point) and improving the bulk density of the fuel. In oneaspect, the mixture of propane and propylene is a mixture of a molefraction of about 50% propane and a mole fraction of about 50%propylene. In some embodiments, the rocket fuel is a mixture of a molefraction of between 40% and 60% propane and a mole fraction of between60% and 40% propene.

Various embodiments provide a rocket propellant comprising a eutecticmixture of a small chain alkane from 1 to 4 carbons and a small chainalkene from 3 to 4 carbons. In some embodiments, the rocket propellantcomprises a eutectic mixture of a small chain alkane from 1 to 3 carbonsand a small chain alkene having 3 carbons. The mixture of the smallchain alkane and the small chain alkene is in a proportion that lowersthe melting of the mixture below the melting point of both the smallchain alkane and small chain alkene.

For example, the rocket propellant can be a eutectic mixture of a molefraction of 67% methane and a mole fraction of 33% propene. In someembodiments, the rocket propellant is a eutectic mixture of a molefraction of between 75% and 60% methane and a mole fraction of between25% and 40% propene. In some embodiments, the rocket propellant is aeutectic mixture of a mole fraction of between 40% and 60% ethane and amole fraction of between 60% and 40% propene.

Some embodiments provide a rocket propellant comprising a eutecticmixture of a small chain alkane from 1 to 4 carbons and a small chainalkane from 2 to 4 carbons. In some embodiments, the rocket propellantcomprises a eutectic mixture of a small chain alkane having 1 carbon anda small chain alkene having 2 or 3 carbons. The mixture of the smallchain alkanes is in a proportion that lowers the melting of the mixturebelow the melting point of each of the small chain alkanes.

For example, the rocket propellant can be a eutectic mixture of a molefraction of about 46% methane and a mole fraction of about 54% ethane.In some embodiments, the rocket propellant is a mixture of a molefraction of between 25% and 75% methane and a mole fraction of between75% and 25% ethane. In some embodiments, the rocket propellant is amixture of a mole fraction of between 20% and 60% methane and a molefraction of between 80% and 40% propane.

These and other novel eutectic mixtures for use as rocket propellantsand in rocket engine systems are described in detail and claimed in thefollowing Drawings, Description, and Claims.

DRAWINGS

The present disclosure will become more fully understood from thedescription and the accompanying drawings, wherein:

FIG. 1 is a table, which illustrates a comparison of the melting pointsand the boiling points of various fuels to coolant sources, inaccordance to various embodiments;

FIG. 2 is a table, which illustrates a comparison of various physicalproperties of various fuels, in accordance with various embodiments;

FIG. 3 is a phase diagram for a mixture of propane and propene, inaccordance with various embodiments;

FIG. 4 is a graph illustrating the change in density of propane andpropene in a eutectic mixture over a change in temperature, inaccordance with various embodiments;

FIG. 5 is a phase diagram for a mixture of ethane and propene, inaccordance with various embodiments;

FIG. 6 is a phase diagram for a mixture of methane and propene, inaccordance with various embodiments;

FIG. 7 is a graph illustrating the change in density of methane andpropene in a eutectic mixture over a change in temperature, inaccordance with various embodiments;

FIG. 8 is a bar graph illustrating the values of specific impulse anddensity impulse for 4 different propellants, in accordance with variousembodiments;

FIG. 9 is a bar graph illustrating the values of specific impulse anddensity impulse for 5 different propellants at a 20:1 expansion ratio,in accordance with various embodiments;

FIG. 10 is a bar graph illustrating the values of specific impulse anddensity impulse for 5 different propellants at a 4000:1 expansion ratio,in accordance with various embodiments;

FIG. 11 is a phase diagram for a mixture of methane and ethane, inaccordance with various embodiments;

FIG. 12 is a graph illustrating the change in density of methane andethane in a eutectic mixture over a change in temperature, in accordancewith various embodiments;

FIG. 13 is a phase diagram for a mixture of methane and propane, inaccordance with various embodiments;

FIG. 14 is a table, which illustrates a comparison of the melting pointof various light hydrocarbons and eutectic mixtures thereof, inaccordance to various embodiments;

FIG. 15 is a table, which illustrates a comparison of the ideal specificimpulse of various light hydrocarbons and eutectic mixtures thereof, inaccordance to various embodiments;

FIG. 16 is a table, which illustrates a comparison of the density ofvarious light hydrocarbons and eutectic mixtures thereof, in accordanceto various embodiments;

FIG. 17 is a bar graph illustrating the values of specific impulse anddensity impulse for 5 different propellants at a 20:1 expansion ratio,in accordance with various embodiments;

FIG. 18 is a schematic drawing illustrating a cross-section of anexemplary rocket system, in accordance with various embodiments.

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of any of the exemplary embodimentsdisclosed herein or any equivalents thereof. It is understood that thedrawings are not drawn to scale. For purposes of clarity, the samereference numbers will be used in the drawings to identify similarelements.

DESCRIPTION

The following description is merely exemplary in nature and is in no wayintended to limit the exemplary embodiments, their application, or uses.It should be understood that steps within a method may be executed indifferent order without altering the principles of the presentdisclosure. For example, various embodiments may be described herein interms of various functional components and processing steps. It shouldbe appreciated that such components and steps may be realized by anynumber of hardware components configured to perform the specifiedfunctions.

Various embodiments provide compositions, which are propellants forrockets, space transportation vehicles, launch vehicles and systems,crew escape vehicles and systems, launch escape towers, and spacevehicle systems and devices. The compositions can be areduced-temperature propellant for improving performance of a rocketstage, a rocket, a space vehicle, and the like. Some embodiments providea system, which can be employed as a rocket engine.

Some embodiments provide a rocket propellant mixture comprising a smallchain alkane mixed with a small chain alkene. The small chain alkane cancomprise from 1 to 4 carbons and the small chain alkene can comprisefrom 3 to 4 carbons. The mixture of the small chain alkane and smallchain alkene is in a proportion that lowers the melting of the mixturebelow the melting point of both the small chain alkane and small chainalkene. In other words, the mixture of the small chain alkane and smallchain alkene is in a proportion, which allows the mixture to be a liquidat a temperature that each of the small chain alkane and the small chainalkene are solids. The rocket propellant mixture can be combined with anoxidizer, such as, liquid oxygen (LOX), in a rocket engine.

The rocket propellant mixture, as described herein, can be cryogenicallychilled to the boiling point of liquid nitrogen (LN) and remain in aliquid state. The rocket propellant mixture can remain in a liquid statewhile in thermal communication with a cryogenic source.

In some embodiments, the rocket propellant mixture comprises propane andpropene (propylene). In one example, the rocket propellant mixtureconsists of propane and propene at a mole fraction 50% for eachcomponent. However, the mixture can consist of propane a mole fractionof between 40% and 60% and propene a mole fraction of between 60% and40%.

In other embodiments, the rocket propellant mixture comprises ethane andpropene. In one example, the rocket propellant mixture consists ofethane and propene at a mole fraction 50% for each component. However,the mixture can consist of ethane in a mole fraction of between 40% and60% and propene in a mole fraction of between 60% and 40%.

In still other embodiments, the rocket propellant mixture comprisesmethane and propene. In one example, the rocket propellant mixtureconsists of methane in a mole fraction of 67% and propene in a molefraction of 33%. However, the mixture can consist of methane in a molefraction of between 75% and 60% and propene in a mole fraction ofbetween 25% and 40%.

Some embodiments provide a rocket propellant comprising a mixture of asmall chain alkane having 1 carbon and a small chain alkene having 2 or3 carbons. The mixture of the small chain alkanes is in a proportionthat lowers the melting of the mixture below the melting point of eachof the small chain alkanes.

In some embodiments, the rocket propellant mixture comprises methane andethane. In one example, the rocket propellant mixture consists ofmethane in a mole fraction of about 46% and ethane in a mole fraction ofabout 54%. However, the rocket propellant mixture can consist of methanein a mole fraction of between 25% and 75% and ethane a mole fraction ofbetween 75% and 25%. In other embodiments, the rocket propellant mixturecan consist of methane in a mole fraction of between 20% and 60% andpropane in a mole fraction of between 80% and 40%.

Turning to FIG. 1, Table 1 is comparison of the melting points andboiling points of various fuels to cooling sources. Although most ofthese fuels can be combined with an oxidizer other than LOX, the focusof this discussion will only on LOX as the oxidizer. As illustrated inTable 1, available coolants are LOX and LN, which can be used to coolthe LOX. In some rocket designs, LOX may not be cooled by LN but ratherLOX is vented to atmosphere and topped off as the level drops. In thesedesigns only LOX is available as a coolant.

As a note to Table 1, RP-1 is Rocket Propellant 1 or Refined Petroleum1, as is well known those skilled in the art. RP-1 is a refined form ofkerosene, which is cheaper than liquid hydrogen (LH) and is stable atroom temperature. Although RP-1 has lower specific impulse (“Isp”) thanLH, RP-1 is far higher density than LH, therefore it is far morepowerful than LH by volume.

Other than LH, all of the listed fuels are solids at the boiling point(77K) of LN. Since the rocket propellant needs to flow from a tank tothe combustion chamber and mix with the LOX, a solid fuel cannot toused. In addition to LH, propane, propene, ethane and maybe even methaneare liquids at the boiling point (90K) of LOX, while all of the otherfuels are solid at the boiling point of LOX. Please note that thedensity of LH is far less than the density of all of the other fuelslisted in Table 1.

From the comparison in Table 1, none of the hydrocarbon (HC) based fuelscan be used as a rocket propellant while in thermal communication withLN. Of the HC fuels listed, most of the small chain HC fuels can be usedcan be used as a rocket propellant while in thermal communication withLOX.

In very unexpected results, the inventors discovered that certain smallchain alkane from 1 to 4 carbons and certain small chain alkene from 3to 4 carbons can be mixed in certain proportions that lowers the meltingof the mixture below the melting point of both the small chain alkaneand small chain alkene. These mixtures are cryogenically compatible withvarious cryogenic coolants and have increased density near the meltingpoint of the mixture. The inventors determined that these mixtures canbe used for rocket propellants.

Now moving to FIG. 2, Table 2 is a performance comparison of variousfuels. In very unexpected results, the inventors discovered that amixture of methane and propene has a eutectic point at certain mixtures,which below the boiling point of LN. This mixture of methane and propenehas an increased density and has physical properties that make itsuperior to RP-1 as a rocket propellant, as shown in FIG. 2.

In very unexpected results, the inventors discovered that a mixture ofpropene and propene has a eutectic point at certain mixtures, whichbelow the boiling point of LN. This mixture of propane and propene hasan increased density and has physical properties that make it superiorto RP-1 as a rocket propellant, as shown in FIG. 2.

A brief review of the table above shows that LOX is thermally compatiblewith both propane and propylene (propene) and that nominally LN isthermally incompatible with methane, propane and propylene. It is notcommonly appreciated that the density of propane and propylene at themelting point makes them excellent rocket fuels, because most propertytables for propane and propylene are calibrated to the normal boilingpoint (NBP) of propane and propylene. Most practicing engineers look atthe density of propane as 0.49 g/cc at the NBP, not the effectivedensity of propane at the melting point of 1.01 g/cc, and fail toappreciate the dramatic density rise of propane as it is subcooledtowards the melting point. The even better density of a propane mix suchas about 50%/50% blend of propane/propylene (Pro/Poly 50) subcooled tonear the NBP of LN where it increases towards 1.06 g/cc, which grants a5% density impulse gain over subcooled propane.

A eutectic mixture of propane and propylene provides over 372 seconds oftheoretical specific impulse, while having a freezing point margin of10K (80K) below the normal atmospheric boiling point of LOX. This fuelcombination then will provide a high specific impulse, and hence areasonable structural mass fraction (SW) and propellant mass fraction(PMF), while keeping tank design simple, tank weights low, and overallstage manufacturing costs reasonable.

In one aspect of the present invention, mixtures of propane/propylene,preferably about a 50%/50% mixture (Pro/Poly 50), exhibit strongreduction in melting point, while a eutectic mixture should exhibit amelting point (about 75 Kelvin (K)) compatible with exposure to liquidnitrogen (LN). Mixtures of propane/propylene can be cooled with LN, LOX,liquid helium or by active mechanical coolers or other methods known toone of ordinary skill in the art.

An enhanced Pro/Poly mix can be mixed at any ratio of propane/propylenewhich results in a reduced melting point down to the eutectic point. Theeutectic point is a mixture of approximately 50% propane/50% propylene+/−5%, and is below the boiling point for LN and calculations indicatesshould have a melting point of about 75 K.

A colder, denser propellant provides a higher density impulse than thesame propellant at the normal boiling point (NBP). A liquid pro/poly 50mixes as liquid phase with LOX providing complete blending beforeignition giving a potential for about 100% combustion efficiency. Adenser propellant reduces pump power requirements to the pump for theequivalent mass flow.

An increase of density impulse increases the performance of a rocketstage, thus lowering the temperatures and freezing points of propellantsresults in higher performance even above the engineering improvementsengendered by thermal compatibility. Pro/Poly 50 will exhibit a bulkdensity of about 1.06 G/cc, and, at about 77 K, LOX increases in densityto about 1.21 g/cc

Some embodiments provide mixtures of propane/propylene and to lower themelting point into the working ranges for LN. This ultimately approachesthe eutectic point wherein the freezing (melting) point of apropane/propylene mixture can be lowered and the viscosity engineered tomeet the requirements of passage through fine cooling passages andthrough a high speed turbopump.

FIG. 3 is a phase diagram for a mixture of propane and propene, whichhas temperature in K on the y-axis and the increasing mole fraction ofpropene on the x-axis. This phase diagram illustrates that any mixtureof propane and propene has a lower melting point (in degrees K) than themelting point for either pure propane or pure propene. The point atwhich a mixture has lowest melting (eutectic point) is indicated on thephase diagram. In addition, the NBP of LN and LOX have been added tothis phase diagram. From an analysis of the phase diagram, the eutecticpoint is at a mole fraction of 50% propane and a mole fraction of 50%propene, which has a melting point of 75.0K. As illustrated on the phasediagram, the eutectic point is below the boiling point of LN and thismixture will remain in a liquid state while in thermal communicationwith LN. As indicated on the phase diagram, other mixtures of propaneand propene have a melting point below the NBP of LN.

Based on the data that generated the phase diagram, at a mole fractionof 45% propane and a mole fraction of 55% propene, the melting point ofthis mixture is 76.27K, which is below the NBP of LN (77.3K).Furthermore, at a mole fraction of 55% propane and a mole fraction of45% propene, the melting point of this mixture is 76.27K, which is alsobelow the NBP of LN (77.3K). These mixtures provide the termini of arange of mixtures of propane and propene that can be used acryogenically LN compatible rocket propellant.

However, at a mole fraction of 60% propane and a mole fraction of 40%propene, the melting point of this mixture is 77.48K, which is slightlyabove the melting point of the NBP of LN (77.3K). At a mole fraction of40% propane and a mole fraction of 60% propene, the melting point ofthis mixture is 77.48K, which is slightly above the melting point of theNBP of LN (77.3K). Since the LN, while in thermal communication withthese mixtures, will not chill the mixtures down to the exact NBP of LN,these mixtures provide the termini for an alternative range of mixturesof propane and propene that can be used a cryogenically LN compatiblerocket propellant. Still further, the combinations of mole fraction of65% and 35% of each component have a melting point of 78.64K, which isslightly higher than the NBP of LN (77.3K). As discussed above, thesemixtures provide the termini for a second alternative range of mixturesof propane and propene that can be used a cryogenically LN compatiblerocket propellant. The combinations of mole fraction of 70% and 30% ofeach component have a melting point of 79.74K, which is also slightlyhigher than the NBP of LN (77.3K). If efficiency of the thermalcommunication of the LN is low, these mixtures provide the termini for athird alternative range of mixtures of propane and propene that can beused a cryogenically LN compatible rocket propellant.

Of course, adding pressure to any of these mixtures, can further reducethe melting point of the mixture. Although high pressure in a tank isnot the best configuration in a rocket engine while in flight. The tankcan be pressurized while the rocket is still on the ground duringprelaunch, which can further lower the melting point of any of thesemixtures. Moving back to FIG. 3, since both propane and propene havemelting points below the NBP of LOX, as illustrated in Table 1 of FIG.1, any mixture of propane and propene will be in a liquid state at theNBP of LOX. If LOX is used as a coolant, any of pure propane, purepropene, or any mixture thereof, can be used a cryogenically LOXcompatible rocket propellant.

Flipping to FIG. 4, a graph illustrates the change in density of propaneand propene at a mixture 50:50 in mole fraction over a change intemperature. The graph has density in the units of kg/m3 on theleft-hand y-axis and density in the units of lbs/ft3 on the right handy-axis. A temperature range from 75K to 100K is on the x-axis. From thisdata, the density of the mixture increases as temperature decreases. Atthe NBP of LN, the density of the mixture is 761.4 kg/m3. The cryogeniccooling of the mixture to below the NBP of LN increases the fueldensity, which increases the performance of this fuel mixture as arocket propellant. The fuel density of this mixture is greater than RP-1

FIG. 5 is a phase diagram for a mixture of ethane and propene, which hastemperature in K on the y-axis and the increasing mole fraction ofpropene on the x-axis. This phase diagram illustrates that any mixtureof ethane and propene has a lower melting point (in degrees K) than themelting point for either pure ethane or pure propene. From an analysisof the phase diagram, the eutectic point is at a mole fraction of 50%ethane and a mole fraction of 50% propene, which has a melting point of75.2K.

As discussed above, other mixtures of ethane and propane are in a liquidstate at the NBP of LN. For example, the combinations of mole fractionof 55% and 45% of each component have a melting point of 76.27K, whichis below than the NBP of LN (77.3K). These mixtures provide the terminiof a range of mixtures of ethane and propene that can be used acryogenically LN compatible rocket propellant. In another example, thecombinations of mole fraction of 60% and 40% of each component have amelting point of 77.48K, which is slightly higher than the NBP of LN(77.3K). As discussed above, these mixtures provide the termini for analternative range of mixtures of methane and propene that can be used acryogenically compatible rocket propellant. In still another example,the combinations of mole fraction of 65% and 35% of each component havea melting point of 78.64K, which is slightly higher than the NBP of LN(77.3K). As discussed above, these mixtures provide the termini for asecond alternative range of mixtures of propane and propene that can beused a cryogenically LN compatible rocket propellant.

The mixture of ethane and propene have a larger disparity in the amountof mole fraction for each component. Factors that can contribute tothese mixtures being useable, are poor efficiency of thermalcommunication between the mixture and the LN and/or pressurization ofthe fuel tank. Of course, there are other factors, which couldcontribute, which are known to those skilled in the art. Since the bothethane and propene are liquid at the NBP of LOX, if LOX is used as acoolant, any of pure propane, pure propene, or any mixture thereof, canbe used a cryogenically LOX compatible rocket propellant.

FIG. 6 is a phase diagram for a mixture of methane and propene, whichhas temperature in K on the y-axis and the increasing mole fraction ofpropene on the x-axis. This phase diagram illustrates that any mixtureof methane and propene has a lower melting point (in degrees K) than themelting point for either pure methane or pure propene. The eutecticpoint, as well as, the NBP of LN and LOX are included in this phasediagram. From an analysis of the phase diagram, the eutectic point is ata mole fraction of 67% methane and a mole fraction of 33% propene, whichhas a melting point of 68.92K.

As discussed above, other mixture of methane and propane are in a liquidstate at the NBP of LN. For example, the mixture of mole fraction of 25%of propene and of 75% methane has a melting point of 77.14K, which isbelow than the NBP of LN (77.3K). The mixture of mole fraction of 55% ofpropene and of 45% methane has a melting point of 76.57K, which is belowthan the NBP of LN (77.3K). These mixtures provide the termini of arange of mixtures of methane and propene that can be used acryogenically compatible rocket propellant. In another example, themixture of mole fraction of 60% of propene and of 40% methane has amelting point of 78.0K, which is slightly higher than the NBP of LN(77.3K). As discussed above, these mixtures provide the termini for analternative range of mixtures of methane and propene that can be used acryogenically LN compatible rocket propellant. In still another example,the mixture of mole fraction of 15% of propene and of 85% methane has amelting point of 80.47K, which is slightly above the NBP of LN (77.3K).As discussed above, these mixtures provide the termini for a secondalternative range of mixtures of propane and propene that can be used acryogenically LN compatible rocket propellant.

The mixture of methane and propene have a larger disparity in the amountof mole fraction for each component. Many factors that can contribute tothese mixtures being useable, as discussed above Since the propene andmaybe methane are liquid at the boiling point of LOX, if LOX is used asa coolant, any of pure propene, or any mixture methane and propene, canbe used a cryogenically LOX compatible rocket propellant.

Flipping to FIG. 7, a graph illustrates the change in density of methaneand propene at a mixture 50:50 in mole fraction over a change intemperature. The graph has density in the units of kg/m3 on theleft-hand y-axis and density in the units of lbs/ft3 on the right handy-axis. A temperature range from 75K to 100K is on the x-axis. From thisdata, the density of the mixture increases as temperature decreases. Atthe boiling point of LN, the density of the mixture is 678.4 kg/m3. Thecryogenic cooling of the mixture to below the boiling point of LNincreases the fuel density, which increases the performance of this fuelmixture as a rocket propellant. The fuel density of this mixture isgreater than RP-1

FIG. 8 is a bar graph having Impulse in seconds on the y-axis and the 4propellants on the x-axis. In this bar graph, the specific impulse andthe density impulse for each of the propellants are indicated by bothbars and the actual number value (in lb/ft3) at the top of the bar.Since RP-1 is the most used rocket propellant, it is on the graph as thecurrent standard. The other propellants on this graph are methane, aeutectic mixture of methane and propene, and a eutectic mixture ofpropane and propene (Pro/Poly 50). The calculations that were used togenerate this graph included the conditions of 1000 psi of chamberpressure, and a nozzle expansion ratio of 100:1.

From analysis of the bar graph, the specific impulse for RP-1 is thelowest of the 4 propellants under these conditions. The specific impulseof the other 3 propellants is very similar ranging from 380 to 385.Moreover, the density impulse for RP-1 is the lowest of the 4propellants. The density impulse of each of the propellants increasesmoving from left to right. There is a significant increase of over 5% ofthe density impulse of the Pro/Poly 50 over the RP-1. According to thedata on the graph, both of the eutectic mixtures are superior to RP-1.In addition, Pro/Poly 50 has almost a 2% increase in specific impulseand over a 5% increase in density impulse as compared to RP-1. Further,the eutectic mixture of methane and propene has over a 2% increase inspecific impulse and over a 4% increase in density impulse as comparedto RP-1.

FIG. 9 is a bar graph having Impulse in seconds on the y-axis and the 5different propellants on the x-axis. In this bar graph, the specificimpulse and the density impulse for each of the propellants areindicated by both bars and the actual number value (in lb/ft3) at thetop of each bar. Since RP-1 is the most used rocket propellant, it is onthe graph as the current standard. The other propellants on this graphare methane, a eutectic mixture of methane and propene, a eutecticmixture of propane and propene (Pro/Poly 50), and liquid hydrogen. Thecalculations that were used to generate this graph used the conditionsof 1000 psi of chamber pressure, and a nozzle expansion ratio of 20:1.

From analysis of the bar graph, the specific impulse (290) for RP-1 isthe lowest of the 5 propellants under these conditions. However, thespecific impulse of the methane, the eutectic mixture of methane andpropene, the eutectic mixture of propane and propene are similar to thespecific impulse for RP-1, ranging from 293 to 299. However, the densityimpulse (302) for the eutectic mixture of propane and propene isslightly better than the density impulse (297) for RP-1 under theseconditions. Although liquid hydrogen has the highest specific impulse(367), the specific density (110) for liquid hydrogen is by far thelowest. According to the data on the graph, Pro/Poly 50 is the bestpropellant compared to the 4 other propellants. In addition, Pro/Poly 50has over 3% increase in specific impulse and almost a 5% increase indensity impulse as compared to RP-1. Further, the eutectic mixture ofmethane and propene has over a 3% increase in specific impulse and a 2%increase in density impulse as compared to RP-1.

FIG. 10 is a bar graph having Impulse in seconds on the y-axis and the 5different propellants on the x-axis. The 5 propellants are the same ason the bar graph of FIG. 9. The calculations that were used to generatethis graph used the conditions of 1000 psi of chamber pressure, and anozzle expansion ratio of 4000:1.

From analysis of the graph, the specific impulse (412) for RP-1 is thelowest of the 5 propellants under these conditions. However, thespecific impulse of the methane, the eutectic mixture of methane andpropene, the eutectic mixture of propane and propene range from 424 to426. In addition, the density impulse (439 and 451) for the eutecticmixtures are slightly better than the density impulse (430) for RP-1under these conditions. Although liquid hydrogen has the highestspecific impulse (502), the specific density (195) for liquid hydrogenis by far the lowest. According to the data on the graph, the eutecticmixtures are the best propellants compared to the other propellants. Inaddition, Pro/Poly 50 is at least 2% better than RP-1 in both specificimpulse and density impulse.

Some embodiments provide a rocket propellant comprising a eutecticmixture of a small chain alkane from 1 to 4 carbons and a small chainalkane from 2 to 4 carbons. In some embodiments, the rocket propellantcomprises a eutectic mixture of a small chain alkane having 1 carbon anda small chain alkene having 2 or 3 carbons. The mixture of the smallchain alkanes is in a proportion that lowers the melting of the mixturebelow the melting point of each of the small chain alkanes.

FIG. 11 is a phase diagram for a mixture of methane and ethane, whichhas temperature in K on the y-axis and the increasing mole fraction ofethane on the x-axis. This phase diagram illustrates that any mixture ofmethane and ethane has a lower melting point (in degrees K) than themelting point for either pure methane or pure ethane. The point at whicha mixture has lowest melting (eutectic point) is indicated on the phasediagram. In addition, the NBP of LN and LOX have been added to thisphase diagram. From an analysis of the phase diagram, the eutectic pointis at a mole fraction of 46% methane and a mole fraction of 54% ethane,which has a melting point of 56.08 K. As illustrated on the phasediagram, the eutectic point is below the NBP of LN and this mixture willremain in a liquid state while in thermal communication with LN. Asindicated on the phase diagram, other mixtures of propane and propenehave a melting point below the NBP of LN.

Based on the data that generated the phase diagram, at a mole fractionof 80% methane and a mole fraction of 20% ethane, the melting point ofthis mixture is 77.14K, which is below the NBP of LN (77.3K).Furthermore, at a mole fraction of 25% methane and a mole fraction of75% ethane, the melting point of this mixture is 73.51K, which is alsobelow the NBP of LN (77.3K). However, at a mole fraction of 20% methaneand a mole fraction of 80% ethane, the melting point of this mixture is78.29, which is just above the NBP of LN (77.3K). These mixtures providethe termini of a range of mixtures of methane and ethane that can beused a cryogenically LN compatible rocket propellant.

In another example, the mixture of a mole fraction of 85% methane and amole fraction of 15% ethane, the melting point of this mixture is80.47K, which is slightly higher than the NBP of LN (77.3K). The mixtureof a mole fraction of 20% methane and a mole fraction of 80% ethane hasa melting point of 78.29K, which is slightly higher than the NBP of LN(77.3K). These mixtures provide the termini for an alternative range ofmixtures of methane and propene that can be used a cryogenicallycompatible rocket propellant.

Turning to FIG. 12, a graph illustrates the change in density of methaneand ethane in a eutectic mixture over a change in temperature. The graphhas density in the units of kg/m3 on the left-hand y-axis and density inthe units of lbs/ft3 on the right-hand y-axis. A temperature range from75K to 100K is on the x-axis. From this data, the density of the mixtureincreases as temperature decreases. At the boiling point of LN, thedensity of the mixture is 575.1 kg/m3. The cryogenic cooling of themixture to below the boiling point of LN increases the fuel density,which increases the performance of this fuel mixture as a rocketpropellant. The fuel density of this mixture is greater than RP-1

FIG. 13 is a is a phase diagram for a mixture of methane and propane,which has temperature in K on the y-axis and the increasing molefraction of propane on the x-axis. This phase diagram illustrates thatany mixture of methane and propane has a lower melting point (in degreesK) than the melting point for either pure methane or pure propane. Froman analysis of the phase diagram, the eutectic point is at a molefraction of 68% methane and a mole fraction of 32% propane, which has amelting point of 69.47K.

Other mixtures of methane and propane are in a liquid state at theboiling point of LN. The mixture of a mole fraction of 80% methane and amole fraction of 20% propane has a melting point of 77.14K, which isbelow the NBP of LN (77.3K). The mixture of a mole fraction of 45%methane and a mole fraction of 55% propane has a melting point of76.24K, which is below the NBP of LN (77.3K). The mixture of a molefraction of 40% methane and a mole fraction of 60% propane has a meltingpoint of 77.48K, which is almost equivalent to the NBP of LN (77.3K).These mixtures provide the termini of a range of mixtures of ethane andpropane that can be used a cryogenically LN compatible rocketpropellant.

In another example, the mixture of a mole fraction of 85% methane and amole fraction of 15% propane has a melting point of 80.47K, which isslightly higher than the NBP of LN (77.3K). The mixture of a molefraction of 35% methane and a mole fraction of 65% propane has a meltingpoint of 78.64K, which is slightly higher than the NBP of LN (77.3K). Asdiscussed above, these mixtures provide the termini for an alternativerange of mixtures of methane and propane that can be used acryogenically compatible rocket propellant.

Moving to FIG. 14, Table 3 illustrates a comparison of the melting pointof various light hydrocarbons and eutectic mixtures thereof. Theeutectic mixture of methane and ethane has a melting point of 56.1K,which is far below LN NBP of 77.3K. Furthermore, the melting points ofeutectic mixtures of methane and propene (68.9K), ethane and propene(75.0K), as well as, propane and propene (75.0), are below LN NBP of77.3K. Under the cryogenic conditions of LN, these eutectic mixtures areliquids.

In FIG. 15, Table 4 illustrates a comparison of the ideal specificimpulse of various light hydrocarbons and eutectic mixtures thereofusing the conditions of 1000 psi of chamber pressure, and a nozzleexpansion ratio of 4000:1. The eutectic mixture of methane and ethanehas a specific impulse of 425.4, which is has over a 3% increase inspecific impulse as compared to RP-1 (412), under the same conditions(See FIG. 10).

In FIG. 16, Table 5 illustrates a comparison of the density (in kg/m3)of various light hydrocarbons and eutectic mixtures thereof at LOX NBP.

FIG. 17 is a bar graph having Impulse in seconds on the y-axis and the 5different propellants on the x-axis. In this bar graph, the specificimpulse and the density impulse for each of the propellants areindicated by both bars and the actual number value (in lb/ft3) at thetop of each bar. As discussed herein, RP-1 is the most used rocketpropellant, it is on the graph as the current standard. The otherpropellants on this graph are methane, a eutectic mixture of methane andethane, a eutectic mixture of propane and propene (Pro/Poly 50), andliquid hydrogen. The calculations that were used to generate this graphused the conditions of 1000 psi of chamber pressure, and a nozzleexpansion ratio of 20:1.

From analysis of the bar graph, the specific impulse (290) for RP-1 isthe lowest of the 5 propellants under these conditions. However, thespecific impulse of the methane, the eutectic mixture of methane andethane, the eutectic mixture of propane and propene are similar to thespecific impulse for RP-1, ranging from 293 to 299. In addition, thedensity impulse (319 and 304) for the eutectic mixtures are slightlybetter than the density impulse (297) for RP-1 under these conditions.Although liquid hydrogen has the highest specific impulse (367), thespecific density (110) for liquid hydrogen is by far the lowest.According to the data on the graph, the eutectic mixture of methane andethane is the best propellant compared to the 4 other propellants. Inaddition, the eutectic mixture of methane and ethane has almost a 3%increase in specific impulse and over 7% increase in density impulse ascompared to RP-1.

Finally, in FIG. 18, schematic drawing illustrates a cross-section of anexemplary rocket engine system. Rocket engine 100 comprises atpropellant tank assembly 103, which comprises a fuel tank 101 and anoxidizer tank 102. A propellant mixture is a eutectic mixture of a smallchain alkane from 1 to 4 carbons and a small chain alkene from 3 to 4carbons or of a small chain alkane from 1 to 4 carbons and a small chainalkane from 2 to 4 carbons (as described herein). The propellant mixtureis stored in the fuel tank 101, which is communication with fuel sourceor vent via valve 105. The LOX is stored in oxidizer tank 102, which isin communication with LOX source or vent via valve 106. The fuel tank101 and the oxidizer tank 102 share common wall 109. The propellant tankassembly 103 can be cooled with LN. An oxidizer pump 113 moves the LOXthrough oxidizer line 112 and the amount of LOX entering into thecombustion chamber 116 is controlled by valve 114. A propellant pump 107moves the propellant mixture through propellant line 107 and the amountof the propellant mixture entering into the combustion chamber 116 iscontrolled by valve 110. The blend of the oxidizer and the propellantmixture is ignited in the combustion chamber 116 and the thrust isdirected through nozzle 120.

Some embodiments provide a reduced-temperature propellant mixture forimproving performance of a rocket stage, rockets, and the like, saidreduced temperature propellant mixture comprising: propane; andpropylene, wherein said propylene and said propane are placed in thermalcommunication in a rocket stage for reduced cost and a smaller rocketstage.

The reduced-temperature propellant mixture can be a mixture of about 50%propane/50% propylene that exhibits a melting point below that of amelting point of pure propane or pure propene and is compatible with aliquid oxidizer. The reduced-temperature propellant mixture can be anymixture of propylene and propane for freezing point suppression. In someconfigurations, the reduced-temperature propellant mixture is cooledwith liquid nitrogen to between 75 K and 88 K to improve performance.

Some embodiments provide reduced-temperature propellant mixture forimproving performance of a rocket stage, rockets, and the like, saidreduced-temperature propellant mixture comprising: propane; propylene;and liquid oxidizer, wherein a mixture of said propane and saidpropylene is maintained in thermal communication with said liquidoxidizer for the purposes of improving a rocket stage.

The mixture of said propane and said propylene is a mixture of about 50%propane/50% propylene, and wherein said mixture of about 50% propane/50%propylene and said liquid oxidizer are cooled below a normal boilingpoint to improve performance. A eutectic mixture of said propane andpolypropylene is cooled to the melting point is the best choice of apropane/propylene fuel combusted with said liquid oxygen subcooled tothat same temperature is the superior operating combination for a rocketpropellant.

Various embodiments of the present invention, a mixture of propane andpropylene makes an improved rocket fuel by lowering the melting point(freezing point) and improving the bulk density of the fuel. In oneaspect, the mixture of propane and propylene is a mixture of a molefraction of about 50% propane and a mole fraction of about 50%propylene. In some embodiments, the rocket fuel is a mixture of a molefraction of between 40% and 60% propane and a mole fraction of between60% and 40% propene.

Various embodiments provide a rocket propellant comprising a eutecticmixture of a small chain alkane from 1 to 4 carbons and a small chainalkene from 3 to 4 carbons. In some embodiments, the rocket propellantcomprises a eutectic mixture of a small chain alkane from 1 to 3 carbonsand a small chain alkene having 3 carbons. The mixture of the smallchain alkane and the small chain alkene is in a proportion that lowersthe melting of the mixture below the melting point of both the smallchain alkane and small chain alkene.

For example, the rocket propellant can be a eutectic mixture of a molefraction of 67% methane and a mole fraction of 33% propene. In someembodiments, the rocket propellant is a eutectic mixture of a molefraction of between 75% and 60% methane and a mole fraction of between25% and 40% propene. In some embodiments, the rocket propellant is aeutectic mixture of a mole fraction of between 40% and 60% ethane and amole fraction of between 60% and 40% propene.

Various embodiments provide a liquid propellant consisting essentiallyof: propane; and propylene, wherein said liquid propellant has a meltingpoint less than a melting point of pure propylene and a melting point ofpure propane.

In some configurations, the liquid propellant can consist essentially ofpropane in a mole fraction of about 50% and propylene in a mole fractionof about 50%. In some configurations, the liquid propellant can consistessentially of propane in a mole fraction in a range from 45% to 55% andpropene in a mole fraction in a range from 45% to 55%. In someconfigurations, the liquid propellant can consist essentially of propanein a mole fraction in a range from 40% to 60% and propene in a molefraction in a range from 40% to 60%. In some configurations, the liquidpropellant can consist essentially of propane in a mole fraction in arange from 35% to 65% and propene in a mole fraction in a range from 35%to 65%.

[0099] In some configurations, the liquid propellant is a liquid whencooled with liquid nitrogen to a temperature between 75K and 88K. Insome configurations, the melting point of the liquid propellant is lessthan 84K. In some configurations, the melting point of the liquidpropellant is less than 80K. In some configurations, the melting pointof the liquid propellant is less than 77K.

In some configurations, the liquid propellant has a bulk density greaterthan 1000 kg/m³ at about 77K. In some configurations, the liquidpropellant has a density impulse greater than 400 seconds at about 77K.

Some embodiments provide a rocket propellant comprising a eutecticmixture of a small chain alkane from 1 to 4 carbons and a small chainalkane from 2 to 4 carbons. In some embodiments, the rocket propellantcomprises a eutectic mixture of a small chain alkane having 1 carbon anda small chain alkene having 2 or 3 carbons. The mixture of the smallchain alkanes is in a proportion that lowers the melting of the mixturebelow the melting point of each of the small chain alkanes.

For example, the rocket propellant can be a eutectic mixture of a molefraction of about 46% methane and a mole fraction of about 54% ethane.In some embodiments, the rocket propellant is a mixture of a molefraction of between 25% and 75% methane and a mole fraction of between75% and 25% ethane. In some embodiments, the rocket propellant is amixture of a mole fraction of between 20% and 60% methane and a molefraction of between 80% and 40% propane.

Various embodiments provide a liquid propellant consisting essentiallyof: methane; and ethane, wherein the liquid propellant has a meltingpoint less than a melting point of pure methane and a melting point ofpure ethane.

In some configurations, the liquid propellant can consist essentially ofsaid methane in a mole fraction of about 46% and said ethane in a molefraction of about 54%. In some configurations, the liquid propellant canconsist essentially of said methane in a mole fraction in a range from40% to 50% and said ethane in a mole fraction in a range from 60% to50%. In some configurations, the liquid propellant can consistessentially of said propane in a mole fraction in a range from 25% to75% and the propene in a mole fraction in a range from 75% to 25%. Insome configurations, the liquid propellant can consist essentially ofsaid methane in a mole fraction in a range from 20% to 80% and saidethane in a mole fraction in a range from 80% to 20%.

In some configurations, the liquid propellant is a liquid when cooledwith liquid nitrogen to a temperature between 75K and 88K. In someconfigurations, the melting point of the liquid propellant is less than84K. In some configurations, the melting point of the liquid propellantis less than 80K. In some configurations, the melting point of theliquid propellant is less than 77K.

Various embodiments provide a rocket engine system comprising: theliquid propellant and a liquid oxidizer. In some configurations, theliquid oxidizer is liquid oxygen at a temperature less than 90K. In someconfigurations, the liquid propellant and the liquid oxidizer areseparated by a common wall. In some configurations, the liquidpropellant and the liquid oxidizer are cryogenically cooled to atemperature less than 80 K. The rocket system can comprise liquidnitrogen configured to cryogenically cool the liquid propellant and theliquid oxidizer to the temperature less than 80 K.

As used herein, the phrase “at least one of A, B, and C” can beconstrued to mean a logical (A or B or C), using a non-exclusive logical“or,” however, can be contrasted to mean (A, B, and C), in addition, canbe construed to mean (A and B) or (A and C) or (B and C). As usedherein, the phrase “A, B and/or C” should be construed to mean (A, B,and C) or alternatively (A or B or C), using a non-exclusive logical“or.”

The present invention has been described above with reference to variousexemplary embodiments and examples, which are not intended to belimiting in describing the full scope of systems and methods of thisinvention. However, those skilled in the art will recognize thatequivalent changes, modifications and variations of the embodiments,materials, systems, and methods may be made within the scope of thepresent invention, with substantially similar results, and are intendedto be included within the scope of the present invention, as set forthin the following claims.

1. A liquid propellant consisting essentially of: methane; and ethane,wherein said liquid propellant has a melting point less than a meltingpoint of pure methane and a melting point of pure ethane.
 2. The liquidpropellant according to claim 1, wherein said methane in a mole fractionof about 46% and said ethane in a mole fraction of about 54%.
 3. Theliquid propellant according to claim 1, wherein said liquid propellantis a liquid when cooled with liquid nitrogen to a temperature between 75Kelvin and 88 Kelvin.
 4. The liquid propellant according to claim 1,wherein said methane in a mole fraction in a range from 40% to 50% andsaid ethane in a mole fraction in a range from 60% to 50%.
 5. The liquidpropellant according to claim 1, wherein said propane in a mole fractionin a range from 25% to 75% and the propene in a mole fraction in a rangefrom 75% to 25%.
 6. The liquid propellant according to claim 1, whereinsaid methane in a mole fraction in a range from 20% to 80% and saidethane in a mole fraction in a range from 80% to 20%.
 7. The liquidpropellant according to claim 1, wherein the melting point of the liquidpropellant is less than 84 Kelvin.
 8. The liquid propellant according toclaim 1, wherein the melting point of the liquid propellant is less than80 Kelvin.
 9. The liquid propellant according to claim 1, wherein themelting point of the liquid propellant is less than 77 Kelvin.
 10. Arocket engine system comprising: the liquid propellant according toclaim 1, and a liquid oxidizer.
 11. The rocket engine system accordingto claim 12, wherein the liquid oxidizer is liquid oxygen at atemperature less than 90 Kelvin.
 12. The rocket engine system accordingto claim 13, wherein the liquid propellant and the liquid oxidizer areseparated by a common wall.
 13. The rocket engine system according toclaim 14, wherein the liquid propellant and the liquid oxidizer arecryogenically cooled to a temperature less than 80 Kelvin.
 14. Therocket system according to claim 15, further comprising liquid nitrogenconfigured to cryogenically cool the liquid propellant and the liquidoxidizer to the temperature less than 80 Kelvin.